System and method for generating shaped ultrawide bandwidth wavelets

ABSTRACT

An ultra-wide band (UWB) waveform generator and encoder for use in a UWB digital communication system. The UWB waveform is made up of a sequence of shaped wavelets. The waveform generator produces multi-amplitude, multi-phase wavelets that are time-constrained, zero mean, and can be orthogonal in phase, yet still have a −10 dB power spectral bandwidth that is larger than the frequency of the peak of the power spectrum In one embodiment, the wavelets are bi-phase wavelets. The encoder multiplies each data bit by an n-bit identifying code, (e.g., a user code), resulting in a group of wavelets corresponding to each data bit. The identifying codeword is passed onto the UWB waveform generator for generation of a UWB waveform that can be transmitted via an antenna.

CROSS REFERENCE TO RELATED PATENT DOCUMENTS

The present application is a continuation application of U.S. patentapplication Ser. No. 09/685,205, filed Oct. 10, 2000, entitled SYSTEMAND METHOD FOR GENERATING ULTRA WIDEBAND PULSES.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to ultra wideband radio communicationsystems, and in particular to methods, systems and devices forgenerating waveforms that include wavelets that are shaped and modulatedto convey digital data over a wireless radio communication channel usingultra wideband signaling techniques.

2. Description of the Background

There are numerous radio communication techniques to transmit digitaldata over a wireless channel. These techniques include those used inmobile telephone systems, pagers, remote data collection systems, andwireless networks for computers, among others. Most conventionalwireless communication techniques modulate the digital data onto ahigh-frequency carrier that is then transmitted via an antenna intospace.

Ultra wideband (UWB) communications systems transmit carrierless highdata rate, low power signals. Since a carrier is not used, it isnecessary that the transmitted waveforms themselves contain theinformation being communicated. Accordingly, conventional UWB systemstransmit pulses, the information to be communicated being contained inthe pulses themselves, and not on a carrier.

Conventional UWB communication systems send a sequence of identicalpulses, the timing of which contains the information being communicated,for example, as described by Fullerton and Cowie (U.S. Pat. No.5,677,927). This technique is known as pulse position modulation (PPM).In a PPM scheme, the information in a pulse is obtained by determiningan arrival time of the pulse at a receiver relative to other pulses. Forexample, given an exemplary time window, if a pulse is received at thebeginning of that time window, the receiver will decode that to mean a‘1’ has been sent, whereas if the pulse is received at the end of thatsame time window, the receiver will decode that to mean that a ‘0’ hasbeen received.

Several problems arise with this technique, however. First, it is not asefficient as other techniques, for example, sending non-inverted andinverted pulses where 3 dB less radiated power is required tocommunicate in the same memory-less Gaussian white noise channel.Second, reflections from objects in the vicinity of the transmitter andreceiver can cause a pulse that was supposed to be at the beginning ofthe time window, to appear in at the end of time window, or even in thetime window of a subsequent pulse.

As a result, it would be advantageous if the data stream to betransmitted could be encoded by changing a shape of the UWB pulse ratherthan a position of the UWB pulse as with conventional systems. Forexample, if the UWB pulses had two possible shapes, a single time framecould be used encode a single bit of data, rather than the two timeframes (i.e., early and late) that would be required by a PPM system. Inthe present UWB communications system, and related co-pendingapplication Ser. No. 09/209,460 filed May 14, 1998, entitled ULTRA WIDEBANDWIDTH SPREAD SPECTRUM COMMUNICATIONS SYSTEM, now issued as U.S. Pat.No. 6,700,939, the entire contents of which being incorporated herein byreference, information is carried by the shape of the pulse, or theshape in combination with its position in the pulse-sequence.

Conventional techniques for generating pulses include a variety oftechniques, for example, networks of transmission lines such as thosedescribed in co-pending application Ser. No. 09/209,460 filed May 14,1998, entitled ULTRA WIDE BANDWIDTH SPREAD SPECTRUM COMMUNICATIONSSYSTEM, now issued as U.S. Pat. No. 6,700,939. One of the problemsassociated with this technique is that the transmission lines take upsizeable space and accordingly, are not amenable to integration on amonolithic integrated circuit. Given that a key targeted use of UWBsystems is for small, handheld mobile devices such as personal digitalassistants (PDAs) and mobile telephones, space is at a premium whendesigning UWB systems. Furthermore, it is highly desirable to integratethe entire radio onto a single monolithic integrated circuit in order tomeet the cost, performance, and volume-production requirements ofconsumer electronics devices.

A key attribute that must be maintained, however, regardless of how theinformation is carried, is that no tones can be present. In other words,the average power spectrum must be smooth and void of any spikes. Ingenerating these UWB pulse streams, however, non-ideal deviceperformance can cause tones to pass through to the antenna and to beradiated. In particular, switches, gates, and analog mixers that areused to generate pulses are well known to be non-ideal devices.Accordingly, leakage is a problem. A signal that is supposed to beblocked at certain times, for example, can continue to leak through.Similarly, non-ideal symmetry in positive and negative voltages orcurrent directions can allow tones be generated or leak through. Inanother example, the output of a mixer can include not only the desiredUWB pulse stream, but also spikes in the frequency domain at the clockfrequency and its harmonics, as well as other noise, due to leakagebetween the RF, LO, and IF ports. This is problematic since one of thedesign objectives is to generate a pulse stream that will not interferewith other communications systems.

Similar problems to those discussed above regarding transmitters arealso encountered in UWB receivers. Mixers are used in UWB receivers tomix the received signal with known waveforms so that the datatransmitted may be decoded. As discussed above, the spectral spikes (DCand otherwise) introduced by the non-ideal analog mixers can makedecoding of only moderately weak signals difficult or impossible.

Furthermore, UWB receivers often suffer from leakage of the UWB signaldriving the mixer. These UWB drive signals can radiate into space and bereceived by the antenna where it can jam the desired UWB signal due toits very close proximity and large amplitude. This reception of thedrive signal being used to decode the received signal can thereforecause a self-jamming condition wherein the desired signal becomesunintelligible.

The challenge, then, as presently recognized, is to develop a highlyintegratable approach for generating shape-modulated wavelet sequencesthat can be used in a UWB communications system to encode, broadcast,receive, and decode a data stream. It would be advantageous if the datastream to be transmitted could be encoded by changing a shape of the UWBpulse rather than a position of the UWB pulse as with conventionalsystems.

Furthermore, the challenge is to build such a wavelet generator wherethe smooth power spectrum calculated by using ideal components, isrealized using non-ideal components. In other words, an approach togenerating and receiving UWB waveforms that does not generate unwantedfrequency domain spikes as a by-product, spikes that are prone tointerfere with other communications devices or cause self-jamming, wouldbe advantageous.

It would also be advantageous if the UWB waveform generation approachwere to minimize the power consumption because many of the targetedapplications for UWB communications are in handheld battery-operatedmobile devices.

SUMMARY OF THE INVENTION

Accordingly, one object of this invention is to provide a novelprogrammable wavelet generator for generating a variety of wavelets foruse in a UWB communication system. Another object of the presentinvention is to provide a novel approach to encoding data onto UWBwavelets by controlling the shape of the wavelets, rather than the timeposition of the wavelets.

The inventors of the present invention have recognized that a highlyintegratable UWB wavelet generator may be designed that uses an analogmixer and a pulse generator to create various shapes of UWB wavelets.The inventors of the present invention have also recognized that asingle UWB wavelet can carry more than one bit of information by varyingthe shape of the wavelet (including magnitude), the position of thewavelet, or both, according to an encoding scheme.

These and other objects are achieved according to the present inventionby providing a novel approach for generating wavelets that is highlyintegratable, and an approach to encoding data onto a UWB wavelet bycontrolling the shape of the wavelet, rather than the time position ofthe wavelet.

The wavelet generator is a circuit which is highly integratable and inone embodiment uses two pulse streams that provide an early pulse andlate pulse respectively, from a pulse generation circuit, that whenmixed with a positive or a negative voltage (from a non-return-to-zero(NRZ) data stream, for example) in a conventional differential mixer,creates a wavelet that is either positive or negative (i.e.,non-inverted or inverted), accordingly. In other embodiments, the datato be encoded and the pulse streams generated by the pulse generator aremanipulated so as to further change the shape of the resultant UWBwavelets. By mixing the pulse streams generated by the pulse generatorwith a stream of NRZ data (positive voltage for a ‘1’, negative voltagefor a ‘0’), a waveform having a sequence wavelets can be created thatcan be transmitted as a UWB signal. In a preferred embodiment, theconventional mixer is a Gilbert cell mixer. In other embodiments, themixer is, for example, a diode bridge mixer, or any electrically,optically, or mechanically-driven configuration of switching devicesincluding, for example, an FET, a bulk semiconductor device, or amicro-machine device.

Consistent with the title of this section, the above summary is notintended to be an exhaustive discussion of all the features orembodiments of the present invention. A more complete, although notnecessarily exhaustive description of the features and embodiments ofthe invention is found in the section entitled “DESCRIPTION OF THEPREFERRED EMBODIMENTS.”

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a block diagram of an ultra-wide band (UWB) transceiver,according to the present invention;

FIG. 1 b is a diagram for illustrating the operation of the transceiverof FIG. 1 a, according to the present invention;

FIG. 2 is a block diagram of the transceiver of FIG. 1 a, thatmanipulates a shape of UWB pulses, according to the present invention;

FIG. 3 is a schematic diagram of a general-purpose microprocessor-basedor digital signal processor-based system, which can be programmedaccording to the teachings of the present invention;

FIG. 4A illustrates a non-return-to-zero data stream bit representing a‘1’ being mixed with an early and a late pulse from a pulse generatoraccording to one embodiment of the present invention;

FIG. 4B illustrates a non-return-to-zero data stream bit representing a‘0’ being mixed with an early and a late pulse from a pulse generatoraccording to one embodiment of the present invention;

FIG. 5A illustrates a single wavelet encoded with a ‘1’ generated by thecircuit FIG. 4A;

FIG. 5B illustrates a single wavelet encoded with a ‘0’ generated by thecircuit FIG. 4B;

FIG. 6 is a schematic diagram of a circuit used to generate an earlypulse and a late pulse according to one embodiment of the presentinvention;

FIG. 6A is a schematic diagram of an AND gate used in the circuit ofFIG. 6 according to one embodiment of the present invention;

FIG. 7A is a schematic diagram of a Gilbert cell differential mixer;

FIG. 7B is an illustration of the early and late pulses generated by thepulse generating circuit of FIG. 6;

FIG. 7C illustrates a bi-phase wavelet generated by the pulse generatingcircuit of FIG. 6 when the incoming data bit is high;

FIG. 7D illustrates a bi-phase wavelet generated by the pulse generatingcircuit of FIG. 6 when the incoming data bit is low;

FIG. 7E is a schematic diagram of a FET bridge differential mixer;

FIG. 7F is a schematic diagram of a diode bridge differential mixer;

FIG. 8A illustrates a non-return-to-zero data stream bit representing a‘1’ being mixed with a mid pulse from a pulse generator on a first inputof a differential port of a mixer and an early and a late pulse from thepulse generator on a second input of a differential port of a mixeraccording to one embodiment of the present invention;

FIG. 8B illustrates a non-return-to-zero data stream bit representing a‘0’ being mixed with a mid pulse from a pulse generator on a first inputof a differential port of a mixer and an early and a late pulse from thepulse generator on a second input of a differential port of a mixeraccording to one embodiment of the present invention;

FIG. 9A illustrates a single wavelet encoded with a ‘1’ generated by thecircuit FIG. 8A;

FIG. 9B illustrates a single wavelet encoded with a ‘0’ generated by thecircuit FIG. 8B;

FIG. 10 illustrates a circuit for creating a constellation of shapes ofUWB wavelets according to one embodiment of the present invention;

FIG. 10A illustrates a circuit for creating a constellation of shapes ofUWB wavelets using a look-up table and D/A converters according to oneembodiment of the present invention;

FIG. 11 illustrates two exemplary waveforms that are summed at thesummer of FIG. 10 according to one embodiment of the present invention;

FIG. 12 illustrates an exemplary constellation of UWB wavelet shapesproduced by the circuit of FIG. 10 according to one embodiment of thepresent invention;

FIGS. 13A-13D illustrate exemplary UWB wavelet shapes wherein data hasbeen further encoded into the amplitude of the wavelets according to oneembodiment of the present invention;

FIGS. 14A-14D illustrate further exemplary UWB wavelet shapes whereindata has been further encoded into the amplitude of the waveletsaccording to one embodiment of the present invention;

FIG. 15 is a schematic of an exemplary digital to analog device foradding amplitude to a waveform according to one embodiment of thepresent invention;

FIG. 16 is a schematic of a UWB wavelet generator for generatingwavelets that include encoding in their amplitude with a digital toanalog device according to one embodiment of the present invention;

FIG. 17 is a schematic of a UWB wavelet generator that generateswavelets having a constellation of shapes according to one embodiment ofthe present invention;

FIG. 18 illustrates an encoding of data with a multi-bit user codeaccording to one embodiment of the present invention; and

FIG. 19 is a schematic of a circuit for encoding non-return-to-zero datawith a user code according to one embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 a is a block diagram of an ultra-wide band (UWB) transceiver. InFIG. 1 a, the transceiver includes three major components, namely,receiver 11, radio controller and interface 9, and transmitter 13.Alternatively, the system may be implemented as a separate receiver 11and radio controller and interface 9, and a separate transmitter 13 andradio controller and interface 9. The radio controller and interface 9serves as a media access control (MAC) interface between the UWBwireless communication functions implemented by the receiver 11 andtransmitter 13 and applications that use the UWB communications channelfor exchanging data with remote devices.

The receiver 11 includes an antenna 1 that converts a UWBelectromagnetic waveform into an electrical signal (or optical signal)for subsequent processing. The UWB signal is generated with a sequenceof shape-modulated wavelets, where the occurrence times of theshape-modulated wavelets may also be modulated. For analog modulation,at least one of the shape control parameters is modulated with theanalog signal. More typically, the wavelets take on M possible shapes.Digital information is encoded to use one or a combination of the Mwavelet shapes and occurrence times to communicate information.

In one embodiment of the present invention, each wavelet communicatesone bit, for example, using two shapes such as bi-phase. In otherembodiments of the present invention, each wavelet may be configured tocommunicate nn bits, where M≧2^(nn). For example, four shapes may beconfigured to communicate two bits, such as with quadrature phase orfour-level amplitude modulation. In another embodiment of the presentinvention, each wavelet is a “chip” in a code sequence, where thesequence, as a group, communicates one or more bits. The code can beM-ary at the chip level, choosing from M possible shapes for each chip.

At the chip, or wavelet level, embodiments of the present inventionproduce UWB waveforms. The UWB waveforms are modulated by a variety oftechniques including but not limited to: (i) bi-phase modulated signals(+1, −1), (ii) multilevel bi-phase signals (+1, −1, +a1, −a1, +a2, −a2,. . . , +aN, −aN), (iii) quadrature phase signals (+1, −1, +j, −j), (iv)multi-phase signals (1, −1, exp(+jπ/N), exp(−jπ/N), exp(+jπ2/N),exp(−jπ2/N), . . . , exp(+j(N−1)/N), exp(−jπ(N−1)/N)), (v) multilevelmulti-phase signals (a_(i) exp(j2πβ/N)|a_(i)∈{1, a1, a2, . . . , aK},β∈{0, 1, . . . , N−1}), (vi) frequency modulated pulses, (vii) pulseposition modulation (PPM) signals (possibly same shape pulse transmittedin different candidate time slots), (viii) M-ary modulated waveformsg_(B) _(i) (t) with B_(i) ∈ {1, . . . , M}, and (ix) any combination ofthe above waveforms, such as multi-phase channel symbols transmittedaccording to a chirping signaling scheme. The present invention,however, is applicable to variations of the above modulation schemes andother modulation schemes (e.g., as described in Lathi, “Modern Digitaland Analog Communications Systems,” Holt, Rinehart and Winston, 1998,the entire contents of which is incorporated by reference herein), aswill be appreciated by those skilled in the relevant art(s).

Some exemplary waveforms and characteristic equations thereof will nowbe described. The time modulation component, for example, can be definedas follows. Let t_(i) be the time spacing between the (i-1)^(th) pulseand the i^(th) pulse. Accordingly, the total time to the i^(th) pulse is$T_{i} = {\sum\limits_{j = 0}^{i}{t_{j}.}}$The signal T_(i) could be encoded for data, part of a spreading code oruser code, or some combination thereof. For example, the signal T_(i)could be equally spaced, or part of a spreading code, where T_(i)corresponds to the zero-crossings of a chirp, i.e., the sequence ofT_(i)'s, and where $T_{i} = \sqrt{\frac{i - a}{k}}$for a predetermined set of a and k. Here, a and k may also be chosenfrom a finite set based on the user code or encoded data.

An embodiment of the present invention can be described using M-arymodulation. Equation 1 below can be used to represent a sequence ofexemplary transmitted or received pulses, where each pulse is a shapemodulated UWB wavelet, g_(B) _(i) (t−T_(i)). $\begin{matrix}{{x(t)} = {\sum\limits_{i = 0}^{\infty}{g_{B_{i}}\left( {t - T_{i}} \right)}}} & (1)\end{matrix}$

In the above equation, the subscript i refers to the i^(th) pulse in thesequence of UWB pulses transmitted or received. The wavelet function ghas M possible shapes, and therefore B_(i) represents a mapping from thedata, to one of the M-ary modulation shapes at the i^(th) pulse in thesequence. The wavelet generator hardware (e.g., the UWB waveformgenerator 17) has several control lines (e.g., coming from the radiocontroller and interface 9) that govern the shape of the wavelet.Therefore, B_(i) can be thought of as including a lookup-table for the Mcombinations of control signals that produce the M desired waveletshapes. The encoder 21 combines the data stream and codes to generatethe M-ary states. Demodulation occurs in the waveform correlator 5 andthe radio controller and interface 9 to recover to the original datastream. Time position and wavelet shape are combined into the pulsesequence to convey information, implement user codes, etc.

In the above case, the signal is comprised of wavelets from i=1 toinfinity. As i is incremented, a wavelet is produced. Equation 2 belowcan be used to represent a generic wavelet pulse function, whose shapecan be changed from pulse to pulse to convey information or implementuser codes, etc.g _(B) _(i) (t)=Re(B _(i,1))·f _(B) _(i,2) _(,B) _(i,3) _(, . . .)(t)+Im(B _(i,1)) ·h _(B) _(i,2) _(,B) _(i,3) _(, . . .) (t)  (2)

In the above equation, function f defines a basic wavelet shape, andfunction h is simply the Hilbert transform of the function f. Theparameter B_(i,1) is a complex number allowing the magnitude and phaseof each wavelet pulse to be adjusted, i.e., B_(i,1)=a_(i)∠θ_(i), wherea_(I) is selected from a finite set of amplitudes and θ_(i) is selectedfrom a finite set of phases. The parameters {B_(i,2), B_(i,3), . . . }represent a generic group of parameters that control the wavelet shape.

An exemplary waveform sequence x(t) can be based on a family of waveletpulse shapes f that are derivatives of a Guassian waveform as defined byEquation 3 below. $\begin{matrix}{{f_{B_{i}}(t)} = {{\Psi\left( {B_{i,2},B_{i,3}} \right)}\left( {\frac{\mathbb{d}^{B_{i,3}}}{\mathbb{d}t^{B_{i,3}}}{\mathbb{e}}^{- {\lbrack{B_{i,2}t}\rbrack}^{2}}} \right)}} & (3)\end{matrix}$

In the above equation, the function Ψ( ) normalizes the peak absolutevalue of f_(B) _(i) (t) to 1. The parameter B_(i,2) controls the pulseduration and center frequency. The parameter B_(i,3) is the number ofderivatives and controls the bandwidth and center frequency.

Another exemplary waveform sequence x(t) can be based on a family ofwavelet pulse shapes f that are Gaussian weighted sinusoidal functions,as described by Equation 4 below.f _(B) _(i,2) _(,B) _(i,3) _(,B) _(i,4) =f _(ω) _(i) _(,k) _(i) _(,b)_(i) (t)=e ^(−[b) ^(i) ^(t]) ² sin (ω_(i) t+k _(i) t ²).   (4)

In the above equation, b_(i) controls the pulse duration, ω_(i) controlsthe center frequency, and k_(i) controls a chirp rate. Other exemplaryweighting functions, beside Gaussian, that are also applicable to thepresent invention include, for example, Rectangular, Hanning, Hamming,Blackman-Harris, Nutall, Taylor, Kaiser, Chebychev, etc.

Another exemplary waveform sequence x(t) can be based on a family ofwavelet pulse shapes f that are inverse-exponentially weightedsinusoidal functions, as described by Equation 5 below. $\begin{matrix}{{{g_{B_{i}}(t)} = {\left( {\frac{1}{{\mathbb{e}}^{\frac{- {({t - {t\quad 1_{f}}}}}{{.3}*t_{r_{i}}}} + 1} - \frac{1}{{\mathbb{e}}^{\frac{- {({t - {t\quad 2_{i}}})}}{{.3}*{tf}_{i}}} + 1}} \right) \cdot {\sin\left( {\theta_{i} + {\omega_{i}t} + {k_{i}t^{2}}} \right)}}}{{{where}\quad\left\{ {B_{i,2},B_{i,3},B_{i,4},B_{i,5},B_{i,6},B_{i,7},B_{i,8}} \right\}} = \left\{ {t_{1_{i}},t_{2_{i}},t_{r_{i}},t_{f_{i}},\theta_{i},\omega_{i},k_{i}} \right\}}} & (5)\end{matrix}$

In the above equation, the leading edge turn on time is controlled byt1, and the turn-on rate is controlled by tr. The trailing edge turn-offtime is controlled by t2, and the turn-off rate is controlled by tf.Assuming the chirp starts at t=0 and T_(D) is the pulse duration, thestarting phase is controlled by θ, the starting frequency is controlledby ω, the chirp rate is controlled by k, and the stopping frequency iscontrolled by ω+kT_(D). An example assignment of parameter values isω=1, tr=tf=0.25, t1=tr/0.51, and t2=T_(D)−tr/9.

A feature of the present invention is that the M-ary parameter set usedto control the wavelet shape is chosen so as to make a UWB signal,wherein the center frequency f_(c) and the bandwidth B of the powerspectrum of g(t) satisfies 2f_(c)>B>0.25f_(c). It should be noted thatconventional equations define in-phase and quadrature signals (e.g.,often referred to as I and Q) as sine and cosine terms. An importantobservation, however, is that this conventional definition is inadequatefor UWB signals. The present invention recognizes that use of suchconventional definition may lead to DC offset problems and inferiorperformance.

Furthermore, such inadequacies get progressively worse as the bandwidthmoves away from 0.25f_(c) and toward 2f_(c). A key attribute of theexemplary wavelets (or e.g., those described in co-pending U.S. patentapplication Ser. No. 09/209,460) is that the parameters are chosen suchthat neither f nor h in Equation 2 above has a DC component, yet f and hexhibit the required wide relative bandwidth for UWB systems.

Similarly, as a result of B>0.25f_(c), it should be noted that thematched filter output of the UWB signal is typically only a few cycles,or even a single cycle. For example, the parameter n in Equation 3 abovemay only take on low values (e.g., such as those described in co-pendingU.S. patent application Ser. No. 09/209,460).

The compressed (i.e., coherent matched filtered) pulse width of a UWBwavelet will now be defined with reference to FIG. 1 b. In FIG. 1 b, thetime domain version of the wavelet thus represents g(t) and the Fouriertransform (FT) version is represented by G(ω). Accordingly, the matchedfilter is represented as G*(ω), the complex conjugate, so that theoutput of the matched filter is P(ω)=G(ω)·G*(ω). The output of thematched filter in the time domain is seen by performing an inverseFourier transform (IFT) on P(ω) so as to obtain p(t), the compressed ormatched filtered pulse. The width of the compressed pulse p(t) isdefined by T_(C), which is the time between the points on the envelopeof the compressed pulse E(t) that are 6 dB below the peak thereof, asshown in FIG. 1 b. The envelope waveform E(t) may be determined byEquation 6 below.E(t)=√{square root over ((p(t))²+(p ^(H)(t))²)}  (6)

where p^(H)(t) is the Hilbert transform of p(t).

Accordingly, the above-noted parameterized waveforms are examples of UWBwavelet functions that can be controlled to communicate information witha large parameter space for making codes with good resultingautocorrelation and cross-correlation functions. For digital modulation,each of the parameters is chosen from a predetermined list according toan encoder that receives the digital data to be communicated. For analogmodulation, at least one parameter is changed dynamically according tosome function (e.g., proportionally) of the analog signal that is to becommunicated.

Referring back to FIG. 1 a, the electrical signals coupled in throughthe antenna 1 are passed to a radio front end 3. Depending on the typeof waveform, the radio front end 3 processes the electric signals sothat the level of the signal and spectral components of the signal aresuitable for processing in the UWB waveform correlator 5. The UWBwaveform correlator 5 correlates the incoming signal (e.g., as modifiedby any spectral shaping, such as a matched filtering, partially matchedfiltering, simply roll-off, etc., accomplished in front end 3) withdifferent candidate signals generated by the receiver 11, so as todetermine when the receiver 11 is synchronized with the received signaland to determine the data that was transmitted.

The timing generator 7 of the receiver 11 operates under control of theradio controller and interface 9 to provide a clock signal that is usedin the correlation process performed in the UWB waveform correlator 5.Moreover, in the receiver 11, the UWB waveform correlator 5 correlatesin time a particular pulse sequence produced at the receiver 11 with thereceive pulse sequence that was coupled in through antenna 1 andmodified by front end 3. When the two such sequences are aligned withone another, the UWB waveform correlator 5 provides high signal to noiseratio (SNR) data to the radio controller and interface 9 for subsequentprocessing. In some circumstances, the output of the UWB waveformcorrelator 5 is the data itself. In other circumstances, the UWBwaveform correlator 5 simply provides an intermediate correlationresult, which the radio controller and interface 9 uses to determine thedata and determine when the receiver 11 is synchronized with theincoming signal.

In some embodiments of the present invention, when synchronization isnot achieved (e.g., during a signal acquisition mode of operation), theradio controller and interface 9 provides a control signal to thereceiver 11 to acquire synchronization. In this way, a sliding of acorrelation window within the UWB waveform correlator 5 is possible byadjustment of the phase and frequency of the output of the timinggenerator 7 of the receiver 11 via a control signal from the radiocontroller and interface 9. The control signal causes the correlationwindow to slide until lock is achieved. The radio controller andinterface 9 is a processor-based unit that is implemented either withhard wired logic, such as in one or more application specific integratedcircuits (ASICs) or in one or more programmable processors.

Once synchronized, the receiver 11 provides data to an input port (“RXData In”) of the radio controller and interface 9. An external process,via an output port (“RX Data Out”) of the radio controller and interface9, may then use this data. The external process may be any one of anumber of processes performed with data that is either received via thereceiver 11 or is to be transmitted via the transmitter 13 to a remotereceiver.

During a transmit mode of operation, the radio controller and interface9 receives source data at an input port (“TX Data In”) from an externalsource. The radio controller and interface 9 then applies the data to anencoder 21 of the transmitter 13 via an output port (“TX Data Out”). Inaddition, the radio controller and interface 9 provides control signalsto the transmitter 13 for use in identifying the signaling sequence ofUWB pulses. In some embodiments of the present invention, the receiver11 and the transmitter 13 functions may use joint resources, such as acommon timing generator and/or a common antenna, for example. Theencoder 21 receives user coding information and data from the radiocontroller and interface 9 and preprocesses the data and coding so as toprovide a timing input for the UWB waveform generator 17, which producesUWB pulses encoded in shape and/or time to convey the data to a remotelocation.

The encoder 21 produces the control signals necessary to generate therequired modulation. For example, the encoder 21 may take a serial bitstream and encode it with a forward error correction (FEC) algorithm(e.g., such as a Reed Solomon code, a Golay code, a Hamming code, aConvolutional code, etc.). The encoder 21 may also interleave the datato guard against burst errors. The encoder 21 may also apply a whiteningfunction to prevent long strings of “ones” or “zeros.” The encoder 21may also apply a user specific spectrum spreading function, such asgenerating a predetermined length chipping code that is sent as a groupto represent a bit (e.g., inverted for a “one” bit and non-inverted fora “zero” bit, etc.). The encoder 21 may divide the serial bit streaminto subsets in order to send multiple bits per wavelet or per chippingcode, and generate a plurality of control signals in order to affect anycombination of the modulation schemes as described above (and/or asdescribed in Lathi).

The radio controller and interface 9 may provide some identification,such as user ID, etc., of the source from which the data on the inputport (“TX Data In”) is received. In one embodiment of the presentinvention, this user ID may be inserted in the transmission sequence, asif it were a header of an information packet. In other embodiments ofthe present invention, the user ID itself may be employed to encode thedata, such that a receiver receiving the transmission would need topostulate or have a priori knowledge of the user ID in order to makesense of the data. For example, the ID may be used to apply a differentamplitude signal (e.g., of amplitude “f”) to a fast modulation controlsignal to be discussed with respect to FIG. 2, as a way of impressingthe encoding onto the signal.

The output from the encoder 21 is applied to a UWB waveform generator17. The UWB waveform generator 17 produces a UWB pulse sequence of pulseshapes at pulse times according to the command signals it receives,which may be one of any number of different schemes. The output from theUWB generator 17 is then provided to an antenna 15, which then transmitsthe UWB energy to a receiver.

In one UWB modulation scheme, the data may be encoded by using therelative spacing of transmission pulses (e.g., PPM, chirp, etc.). Inother UWB modulation schemes, the data may be encoded by exploiting theshape of the pulses as described above (and/or as described in Lathi. Itshould be noted that the present invention is able to combine timemodulation (e.g., such as pulse position modulation, chirp, etc.) withother modulation schemes that manipulate the shape of the pulses.

There are numerous advantages to the above capability, such ascommunicating more than one data bit per symbol transmitted from thetransmitter 13, etc. An often even more important quality, however, isthe application of such technique to implement spread-spectrum,multi-user systems, which require multiple spreading codes (e.g., suchas each with spike autocorrelation functions, and jointly with low peakcross-correlation functions, etc.).

In addition, combining timing, phase, frequency, and amplitudemodulation adds extra degrees of freedom to the spreading codefunctions, allowing greater optimization of the cross-correlation andautocorrelation characteristics. As a result of the improvedautocorrelation and cross-correlation characteristics, the systemaccording to the present invention has improved capability, allowingmany transceiver units to operate in close proximity without sufferingfrom interference from one another.

FIG. 2 is a block diagram of a transceiver embodiment of the presentinvention in which the modulation scheme employed is able to manipulatethe shape and time of the UWB pulses. In FIG. 2, when receiving energythrough the antenna 1, 15 (e.g., corresponding antennas 1 and 15 of FIG.1 a) the energy is coupled in to a transmit/receive (T/R) switch 27,which passes the energy to a radio front end 3. The radio front end 3filters, extracts noise, and adjusts the amplitude of the signal beforeproviding the same to a splitter 29. The splitter 29 divides the signalup into one of N different signals and applies the N different signalsto different tracking correlators 31 ₁-31 _(N). Each of the trackingcorrelators 31 ₁-31 _(N) receives a clock input signal from a respectivetiming generator 7 ₁-7 _(N) of a timing generator module 7, 19, as shownin FIG. 2.

The timing generators 7 ₁-7 _(N), for example, receive a phase andfrequency adjustment signal, as shown in FIG. 2, but may also receive afast modulation signal or other control signal(s) as well. The radiocontroller and interface 9 provides the control signals, such as phase,frequency and fast modulation signals, etc., to the timing generatormodule 7, 19, for time synchronization and modulation control. The fastmodulation control signal may be used to implement, for example, chirpwaveforms, PPM waveforms, such as fast time scale PPM waveforms, etc.

The radio controller and interface 9 also provides control signals to,for example, the encoder 21, the waveform generator 17, the filters 23,the amplifier 25, the T/R switch 27, the front end 3, the trackingcorrelators 31 ₁-31 _(N) (corresponding to the UWB waveform correlator 5of FIG. 1 a), etc., for controlling, for example, amplifier gains,signal waveforms, filter passbands and notch functions, alternativedemodulation and detecting processes, user codes, spreading codes, covercodes, etc.

During signal acquisition, the radio controller and interface 9 adjuststhe phase input of, for example, the timing generator 7 ₁, in an attemptfor the tracking correlator 31 ₁ to identify and the match the timing ofthe signal produced at the receiver with the timing of the arrivingsignal. When the received signal and the locally generated signalcoincide in time with one another, the radio controller and interface 9senses the high signal strength or high SNR and begins to track, so thatthe receiver is synchronized with the received signal.

Once synchronized, the receiver will operate in a tracking mode, wherethe timing generator 7 ₁ is adjusted by way of a continuing series ofphase adjustments to counteract any differences in timing of the timinggenerator 7 ₁ and the incoming signal. However, a feature of the presentinvention is that by sensing the mean of the phase adjustments over aknown period of time, the radio controller and interface 9 adjusts thefrequency of the timing generator 7 ₁ so that the mean of the phaseadjustments becomes zero. The frequency is adjusted in this instancebecause it is clear from the pattern of phase adjustments that there isa frequency offset between the timing generator 7 ₁ and the clocking ofthe received signal. Similar operations may be performed on timinggenerators 7 ₂-7 _(N), so that each receiver can recover the signaldelayed by different amounts, such as the delays caused by multipath(i.e., scattering along different paths via reflecting off of localobjects).

A feature of the transceiver in FIG. 2 is that it includes a pluralityof tracking correlators 31 ₁-31 _(N). By providing a plurality oftracking correlators, several advantages are obtained. First, it ispossible to achieve synchronization more quickly (i.e., by operatingparallel sets of correlation arms to find strong SNR points overdifferent code-wheel segments). Second, during a receive mode ofoperation, the multiple arms can resolve and lock onto differentmultipath components of a signal. Through coherent addition, the UWBcommunication system uses the energy from the different multipath signalcomponents to reinforce the received signal, thereby improving signal tonoise ratio. Third, by providing a plurality of tracking correlatorarms, it is also possible to use one arm to continuously scan thechannel for a better signal than is being received on other arms.

In one embodiment of the present invention, if and when the scanning armfinds a multipath term with higher SNR than another arm that is beingused to demodulate data, the role of the arms is switched (i.e., the armwith the higher SNR is used to demodulate data, while the arm with thelower SNR begins searching). In this way, the communications systemdynamically adapts to changing channel conditions.

The radio controller and interface 9 receives the information from thedifferent tracking correlators 31 ₁-31 _(N) and decodes the data. Theradio controller and interface 9 also provides control signals forcontrolling the front end 3, e.g., such as gain, filter selection,filter adaptation, etc., and adjusting the synchronization and trackingoperations by way of the timing generator module 7, 19.

In addition, the radio controller and interface 9 serves as an interfacebetween the communication link feature of the present invention andother higher level applications that will use the wireless UWBcommunication link for performing other functions. Some of thesefunctions would include, for example, performing range-findingoperations, wireless telephony, file sharing, personal digital assistant(PDA) functions, embedded control functions, location-findingoperations, etc.

On the transmit portion of the transceiver shown in FIG. 2, a timinggenerator 7 ₀ also receives phase, frequency and/or fast modulationadjustment signals for use in encoding a UWB waveform from the radiocontroller and interface 9. Data and user codes (via a control signal)are provided to the encoder 21, which in the case of an embodiment ofthe present invention utilizing time-modulation, passes command signals(e.g., Δt) to the timing generator 7 ₀ for providing the time at whichto send a pulse. In this way, encoding of the data into the transmittedwaveform may be performed.

When the shape of the different pulses are modulated according to thedata and/or codes, the encoder 21 produces the command signals as a wayto select different shapes for generating particular waveforms in thewaveform generator 17. For example, the data may be grouped in multipledata bits per channel symbol. The waveform generator 17 then producesthe requested waveform at a particular time as indicated by the timinggenerator 7 ₀. The output of the waveform generator is then filtered infilter 23 and amplified in amplifier 25 before being transmitted viaantenna 1, 15 by way of the T/R switch 27.

In another embodiment of the present invention, the transmit power isset low enough that the transmitter and receiver are simply alternatelypowered down without need for the T/R switch 27. Also, in someembodiments of the present invention, neither the filter 23 nor theamplifier 25 is needed, because the desired power level and spectrum isdirectly useable from the waveform generator 17. In addition, thefilters 23 and the amplifier 25 may be included in the waveformgenerator 17 depending on the implementation of the present invention.

A feature of the UWB communications system disclosed, is that thetransmitted waveform x(t) can be made to have a nearly continuous powerflow, for example, by using a high chipping rate, where the waveletsg(t) are placed nearly back-to-back. This configuration allows thesystem to operate at low peak voltages, yet produce ample averagetransmit power to operate effectively. As a result, sub-micron geometryCMOS switches, for example, running at one-volt levels, can be used todirectly drive antenna 1, 15, such that the amplifier 25 is notrequired. In this way, the entire radio can be integrated on a singlemonolithic integrated circuit.

Under certain operating conditions, the system can be operated withoutthe filters 23. If, however, the system is to be operated, for example,with another radio system, the filters 23 can be used to provide a notchfunction to limit interference with other radio systems. In this way,the system can operate simultaneously with other radio systems,providing advantages over conventional devices that use avalanching typedevices connected straight to an antenna, such that it is difficult toinclude filters therein.

The UWB transceiver of FIGS. 1 a or 2 may be used to perform a radiotransport function for interfacing with different applications as partof a stacked protocol architecture. In such a configuration, the UWBtransceiver performs signal creation, transmission and receptionfunctions as a communications service to applications that send data tothe transceiver and receive data from the transceiver much like a wiredI/O port. Moreover, the UWB transceiver may be used to provide awireless communications function to any one of a variety of devices thatmay include interconnection to other devices either by way of wiredtechnology or wireless technology. Thus, the UWB transceiver of FIG. 1 aor 2 may be used as part of a local area network (LAN) connecting fixedstructures or as part of a wireless personal area network (WPAN)connecting mobile devices, for example. In any such implementation, allor a portion of the present invention may be conveniently implemented ina microprocessor system using conventional general purposemicroprocessors programmed according to the teachings of the presentinvention, as will be apparent to those skilled in the microprocessorsystems art. Appropriate software can be readily prepared by programmersof ordinary skill based on the teachings of the present disclosure, aswill be apparent to those skilled in the software art.

FIG. 3 illustrates a processor system 301 upon which an embodimentaccording to the present invention may be implemented. The system 301includes a bus 303 or other communication mechanism for communicatinginformation, and a processor 305 coupled with the bus 303 for processingthe information. The processor system 301 also includes a main memory307, such as a random access memory (RAM) or other dynamic storagedevice (e.g., dynamic RAM (DRAM), static RAM (SRAM), synchronous DRAM(SDRAM), flash RAM), coupled to the bus 303 for storing information andinstructions to be executed by the processor 305. In addition, a mainmemory 307 may be used for storing temporary variables or otherintermediate information during execution of instructions to be executedby the processor 305. The system 301 further includes a read only memory(ROM) 309 or other static storage device (e.g., programmable ROM (PROM),erasable PROM (EPROM), and electrically erasable PROM (EEPROM)) coupledto the bus 303 for storing static information and instructions for theprocessor 305. A storage device 311, such as a magnetic disk or opticaldisc, is provided and coupled to the bus 303 for storing information andinstructions.

The processor system 301 may also include special purpose logic devices(e.g., application specific integrated circuits (ASICs)) or configurablelogic devices (e.g, simple programmable logic devices (SPLDs), complexprogrammable logic devices (CPLDs), or re-programmable fieldprogrammable gate arrays (FPGAs)). Other removable media devices (e.g.,a compact disc, a tape, and a removable magneto-optical media) or fixed,high density media drives, may be added to the system 301 using anappropriate device bus (e.g., a small system interface (SCSI) bus, anenhanced integrated device electronics (IDE) bus, or an ultra-directmemory access (DMA) bus). The system 301 may additionally include acompact disc reader, a compact disc reader-writer unit, or a compactdisc juke box, each of which may be connected to the same device bus oranother device bus.

The processor system 301 may be coupled via the bus 303 to a display313, such as a cathode ray tube (CRT) or liquid crystal display (LCD) orthe like, for displaying information to a system user. The display 313may be controlled by a display or graphics card. The processor system301 includes input devices, such as a keyboard or keypad 315 and acursor control 317, for communicating information and command selectionsto the processor 305. The cursor control 317, for example, is a mouse, atrackball, or cursor direction keys for communicating directioninformation and command selections to the processor 305 and forcontrolling cursor movement on the display 313. In addition, a printermay provide printed listings of the data structures or any other datastored and/or generated by the processor system 301.

The processor system 301 performs a portion or all of the processingsteps of the invention in response to the processor 305 executing one ormore sequences of one or more instructions contained in a memory, suchas the main memory 307. Such instructions may be read into the mainmemory 307 from another computer-readable medium, such as a storagedevice 311. One or more processors in a multi-processing arrangement mayalso be employed to execute the sequences of instructions contained inthe main memory 307. In alternative embodiments, hard-wired circuitrymay be used in place of or in combination with software instructions.Thus, embodiments are not limited to any specific combination ofhardware circuitry and software.

As stated above, the processor system 301 includes at least one computerreadable medium or memory programmed according to the teachings of theinvention and for containing data structures, tables, records, or otherdata described herein. Stored on any one or on a combination of computerreadable media, the present invention includes software for controllingthe system 301, for driving a device or devices for implementing theinvention, and for enabling the system 301 to interact with a humanuser. Such software may include, but is not limited to, device drivers,operating systems, development tools, and applications software. Suchcomputer readable media further includes the computer program product ofthe present invention for performing all or a portion (if processing isdistributed) of the processing performed in implementing the invention.

The computer code devices of the present invention may be anyinterpreted or executable code mechanism, including but not limited toscripts, interpretable programs, dynamic link libraries, Java or otherobject oriented classes, and complete executable programs. Moreover,parts of the processing of the present invention may be distributed forbetter performance, reliability, and/or cost.

The term “computer readable medium” as used herein refers to any mediumthat participates in providing instructions to the processor 305 forexecution. A computer readable medium may take many forms, including butnot limited to, non-volatile media, volatile media, and transmissionmedia. Non-volatile media includes, for example, optical, magneticdisks, and magneto-optical disks, such as the storage device 311.Volatile media includes dynamic memory, such as the main memory 307.Transmission media includes coaxial cables, copper wire and fiberoptics, including the wires that comprise the bus 303. Transmissionmedia may also take the form of acoustic or light waves, such as thosegenerated during radio wave and infrared data communications.

Common forms of computer readable media include, for example, harddisks, floppy disks, tape, magneto-optical disks, PROMs (EPROM, EEPROM,Flash EPROM), DRAM, SRAM, SDRAM, or any other magnetic medium, compactdisks (e.g., CD-ROM), or any other optical medium, punch cards, papertape, or other physical medium with patterns of holes, a carrier wave,carrierless transmissions, or any other medium from which a system canread.

Various forms of computer readable media may be involved in providingone or more sequences of one or more instructions to the processor 305for execution. For example, the instructions may initially be carried ona magnetic disk of a remote computer. The remote computer can load theinstructions for implementing all or a portion of the present inventionremotely into a dynamic memory and send the instructions over atelephone line using a modem. A modem local to system 301 may receivethe data on the telephone line and use an infrared transmitter toconvert the data to an infrared signal. An infrared detector coupled tothe bus 303 can receive the data carried in the infrared signal andplace the data on the bus 303. The bus 303 carries the data to the mainmemory 307, from which the processor 305 retrieves and executes theinstructions. The instructions received by the main memory 307 mayoptionally be stored on a storage device 311 either before or afterexecution by the processor 305.

The processor system 301 also includes a communication interface 319coupled to the bus 303. The communications interface 319 provides atwo-way UWB data communication coupling to a network link 321 that isconnected to a communications network 323 such as a local network (LAN)or personal area network (PAN) 323. For example, the communicationinterface 319 may be a network interface card to attach to any packetswitched UWB-enabled personal area network (PAN) 323. As anotherexample, the communication interface 319 may be a UWB accessibleasymmetrical digital subscriber line (ADSL) card, an integrated servicesdigital network (ISDN) card, or a modem to provide a data communicationconnection to a corresponding type of communications line. Thecommunications interface 319 may also include the hardware to provide atwo-way wireless communications coupling other than a UWB coupling, or ahardwired coupling to the network link 321. Thus, the communicationsinterface 319 may incorporate the UWB transceiver of FIG. 2 as part of auniversal interface that includes hardwired and non-UWB wirelesscommunications coupling to the network link 321.

The network link 321 typically provides data communication through oneor more networks to other data devices. For example, the network link321 may provide a connection through a LAN to a host computer 325 or todata equipment operated by a service provider, which provides datacommunication services through an IP (Internet Protocol) network 327.Moreover, the network link 321 may provide a connection through a PAN323 to a mobile device 329 such as a personal digital assistant (PDA)laptop computer, or cellular telephone. The LAN/PAN communicationsnetwork 323 and IP network 327 both use electrical, electromagnetic oroptical signals that carry digital data streams. The signals through thevarious networks and the signals on the network link 321 and through thecommunication interface 319, which carry the digital data to and fromthe system 301, are exemplary forms of carrier waves transporting theinformation. The processor system 301 can transmit notifications andreceive data, including program code, through the network(s), thenetwork link 321 and the communication interface 319.

The encoder 21 and waveform generator 17 of the transceiver of thepresent invention function together to create a UWB waveform from adigital data stream by first multiplying each bit of data in the datastream by an identifying code (e.g., an n-bit user code), therebyexpanding each bit of data into a codeword of data bits equal in lengthto the length of the identifying code. In one embodiment, the codewordis then further processed to create two derivative codewords that arethat are sent to the UWB waveform generator 17 where they are mixed witha pulse generator and recombined through a two-stage mixing processprior to being transmitted via the antenna 15.

As stated above, the encoder 21 receives a digital data stream from anexternal source via the radio and controller interface 9. The encoder 21multiplies each bit of the digital data stream by a user code, which inone embodiment is a unique sequence of bits corresponding to aparticular user. For example, multiplying a user code of ‘1101 0110’ bya data bit of ‘1’ results in an 8-chip representation of the ‘1’ that isidentical to the user code, or ‘1101 0110.’ On the other hand,multiplying that same user code by a data bit of ‘0’ results in an 8-bitrepresentation of the ‘0’ that is the 8 chip user code inverted, or‘0010 1001.’

Continuing with the above example, the encoder 21 multiplies the usercode by each bit of the digital data stream to create a sequence ofn-chip codewords, where n is the length of the user code. Once thedigital data stream has been encoded, the UWB waveform generator 17further processes the sequence of codewords in creating an UWB waveformthat can be transmitted.

FIGS. 4A and 4B illustrate an exemplary circuit using a differentialmixer 401 for generating UWB wavelets encoded with data according to oneembodiment of the present invention. As shown in FIGS. 4A and 4B, abinary non-return-to-zero (NRZ) data source is connected to an input ofa differential mixer 400. Connected to the two differential inputs ofthe LO port 407, 408 of the differential mixer 401 are two outputs of apulse generator that generates a pair of pulse streams configured toapply an early pulse 403 at the first differential input 407 andimmediately thereafter, a late pulse 404 at the second differentialinput 408 of the LO port. The wavelet generator is configured such thatthe NRZ data source is at a rate such that each bit of data will be aslong or longer than the combined duration of an early pulse and a latepulse generated by the pulse generator. Accordingly, each bit of NRZdata will be mixed with both the early pulse 403 and the late pulse 404.

FIG. 4A illustrates the example where the incoming bit from the NRZ datasource is a ‘1’ (i.e., positive voltage), whereas FIG. 4B illustratesthe example where the incoming data bit is a ‘0’ (i.e., negativevoltage). The output of the differential mixer 402 for both examples isa UWB wavelet that occupies the same time frame and has the data encodedin the shape of the wavelet, not in the time position of the wavelet.

FIGS. 5A and 5B illustrate the shapes of the UWB wavelets produced bythe differential mixer 401 in the two examples described in FIGS. 4A and4B respectively. As shown in FIG. 5A, a UWB wavelet 500 is produced bymixing a NRZ data ‘1’ with the early pulse input to the firstdifferential input of the mixer 407 and the late pulse input to thesecond differential input of the mixer 408 as illustrated by FIG. 4A. Aswill be described below, the early and late pulses generated by a pulsegenerator cause the mixer to produce a ‘high’ then ‘low’ output that,when mixed with a NRZ data ‘1,’ will produce the wavelet shown in FIG.5A. As would be well understood by one of ordinary skill in thecommunications art, the shape of the resultant UWB wavelet is such thatthe integral of the wavelet is 0.

FIG. 5B illustrates a UWB wavelet 501 produced by mixing a NRZ data ‘0’(e.g., a negative voltage) with the early pulse input to the firstdifferential input of the mixer 407 and the late pulse input to thesecond differential input of the mixer 408 as illustrated by FIG. 4B. Asshown in FIGS. 5A and 5B, the two different UWB wavelets are invertedrepresentations of one another. By encoding the data (i.e., the ‘0’ andthe ‘1’) onto the shape of the UWB wavelet, the single bit ofinformation may be encoded as one of the two shapes corresponding to a‘0’ or a ‘1’ accordingly. Comparing this novel UWB modulation techniquewith that of a conventional PPM UWB systems, it can be seen that byusing this technique, a bit of information may be transmitted in thetime taken to transmit a single wavelet (i.e., a ‘1’ being a positivethen negative wavelet and a ‘0’ being a negative then positive wavelet),as compared to the necessarily longer time required to transmit atime-positioned encoded bit of information (i.e., a ‘1’ beingrepresented by a wavelet occurring early in a larger time window, and a‘0’ being represented by a wavelet occurring late in a larger timewindow).

FIG. 6 is a schematic diagram of a circuit for generating a UWB waveformin one embodiment of the present invention. As shown in FIG. 6, data 416is mixed at a first mixer 701 with the outputs of an early/late pulsegenerator 200. The early/late pulse streams run at the chipping rate.The chipping rate can be the same as the data rate of derived input data416, in which case a single wavelet, or chip, is transmitted for eachbit. The chipping rate may also be an integer multiple of the data rateof the derived input data 416. In such a case, each bit is made up of apredetermined number of bits. For example, if the data stream 416 is at50 Mb/s and there are 16 chips per bit, then the early/late pulsestreams 286, 288 are at 800 MHz.

As shown in FIG. 6, the pulse generator 200 receives its input from adifferential clock 210 which generates a pulse 203, which isdifferentially transmitted on lines 202 and 204. Input lines 202, 204feed into the first of a set of seven buffers 212, 214, 216, 218, 220,222, and 224 connected in series. While seven buffers are shown in thisfirst series-connected set of buffers, it would be understood by one ofordinary skill in the art that other numbers of buffers could be used toprovide a different time delay through the set. Buffers 214 and 216 areconnected in series via lines 224, 226. In the preferred embodimentdisclosed in FIG. 6, data lines 228 and 230 branch off from lines 224and 226 respectively and serve as inputs to buffer 244. The output ofbuffers 242 and 244 serve as inputs via lines 246, 248 to an exclusiveOR gate 250, which generates a pulse 205. In another embodiment, an ANDgate could be used in place of the exclusive OR gate 250, where theinverting output of one of either buffer 242 or buffer 244 is used tofeed the AND gate 600 instead of the non-inverting output, as shown inFIG. 6A. An AND gate 600 provides some advantages since the AND gate 600generates a pulse only on the rise of the pulse, whereas an exclusive ORgate 250 gives a pulse both on the rise and the fall of the pulse.Therefore, timing of the circuit is less difficult to implement with anAND gate. The output of the exclusive OR gate 250 is a differentialpulse 205 which feeds into another series-connected set of buffers, inthis example, seven buffers 260, 262, 264, 266, 268, 270, and 282 vialines 252, 254. Buffers 262 and 264 are connected in series via lines253 and 255. In the preferred embodiment disclosed in FIG. 6, data lines276 and 278 branch off from lines 253 and 255 respectively and serve asinputs to buffer 280. The output from buffers 280 and 282 feed intodifferential mixer 701 via lines 286 and 288. The differential mixer 701receives the data stream from encoder 21 over lines 292, 294.

The function of the pulse generator 200 shown in FIG. 6 will now bedescribed. The clock 210 generates a differential semi-square wave clocksignal 203, which are transmitted over lines 202, 204 to buffer 212.Buffer 212 serves to amplify, saturate, and generally square up theincoming signal, and then buffer 214 squares it up some more. Thetransmission of the clock signal 203 through two paths, one throughbuffers 216, 218, 220, 222, and 242, and the other through buffer 244,causes the clock signal to reach the output of buffer 244 before itreaches the output of buffer 242. In other words, the output of buffer244 leads the output of buffer 242 by the delay accumulated in buffers216, 218, 220, and 222. Since the inputs to the exclusive OR gate 250are matched except at the clock transitions, pulse 205 is generated atthe output of exclusive OR gate 250 at each transition of the clock. Thepulse stream, therefore, is at twice the clock frequency because anexclusive OR gate 250 generates a pulse on both leading and trailingclock transitions.

In another embodiment, an AND gate 600 could be used in place of theexclusive OR gate 250, where the inverting output of either buffer 242or buffer 244 is used to feed the AND gate 600 instead of thenon-inverting output, as shown in FIG. 6A. Since the inputs to the ANDgate 600 are mismatched except at the leading clock edge transition (ifthe inverting output of buffer 242 is used), or the trailing clock edgetransition (if the inverting output of buffer 244 is used) the output ofthe AND gate 600 is a pulse stream that equals the clock frequency. AnAND gate 600 provides some advantages since the AND gate 600 generates apulse only on the rise or fall of the pulse, whereas an exclusive ORgate 250 gives a pulse both on the rise and the fall of the pulse.Therefore, the duty-cycle of the clock does not have to be exactly 50%in order to have an equal time period between all pulses. Instead, theduty cycle can be anything, making the circuit is less difficult toimplement.

The pulse 205 is transmitted over differential lines 252 and 254 tobuffer 260. Buffer 260 serves to amplify, saturate, and generally squareup the pulse and then buffer 262 squares it up some more. Thetransmission of the pulse 205 through two paths, one path viadifferential lines 253 and 255 through buffers 264, 266, 268, 270, and282, and the other path via differential lines 246 and 248 throughbuffer 280 causes the pulse 205 to reach the output of buffer 280 beforeit reaches the output of buffer 282. In other words, output 286 ofbuffer 280 leads output 288 of buffer 282 by the delay accumulated inbuffers 264, 266, 268, and 270. Accordingly, line 286 has an early pulseand line 288 has a late pulse, making pulse streams 203 a and 203 brespectively.

The early pulse on line 286 feeds the non-inverting differential LOinput of multiplier 701. The late pulse on line 288 feeds the invertingdifferential LO input of multiplier 701. The differential data-source416 generates data, which is differentially transmitted on lines 292 and294. Input lines 292 and 294 feed into the first of a set of twoseries-connected buffers 296 and 298. The differential output data frombuffer 298 drives the differential RF-input port of multiplier 701.Given the data on the RF-port of multiplier 701, and the early and latepulse on the non-inverting and inverting input lines of the differentialLO-port of multiplier 701, the output of the multiplier is the desiredwavelet shape. When the data is a ‘1,’ the output wavelet has aground-positive-negative-ground shape, and when the data is a ‘0,’ theoutput wavelet has a ground-negative-positive-ground shape.

FIG. 7A is a schematic diagram of a transistor-based Gilbert celldifferential mixer used in one embodiment of the present invention. Inthis embodiment, it is shown that mixing the resultant early/late pulsestreams 286, 288 generated by the pulse generator 200 shown in FIG. 6,the result is a sequence of bi-phase wavelets corresponding to the inputdata 416. In other embodiments of the present invention, the waveletsgenerated may have different shapes, such as, but not limited tomultilevel and/or quad-phase wavelets. Accordingly, if differentencoding schemes are used, different amounts of information may beencoded in any single wavelet, thereby affecting the data ratesachievable at a given chip rate.

As would be understood by one of ordinary skill in the art, FIG. 7A is aschematic diagram of a bipolar transistor-based Gilbert celldifferential multiplier. It is capable of multiplying the differentialsignal across 330 and 332, by the differential signal across 286 and288, the product appearing across the differential output 340 and 342.It includes a current mirror 704, which provides a current that will besteered between the differential output nodes 340 and 342. Differentialpair 706 steers the current between two paths, the first path todifferential pair 710, and the second path to differential pair 708.Differential pair 710 and differential pair 708 are connected todifferential input lines 330 and 332, and to the differential outputnodes 340 and 342 so as to oppose one another, (i.e., if thedifferential input 330 is high, then differential pair 710 steers itscurrent to pull 342 low but differential pair 708 steers its current topull 342 high). The pair that dominates is determined by which has themost current available to it, which is determined by differential pair706. Differential pair 706 accepts differential inputs 286 and 288. When286 is higher than 288, the current is steered to differential pair 710and the output 340 is inverted from input 330 (i.e., multiplying by −1).When 288 is higher than 286, the current is steered to differential pair708 and the output 340 is not inverted from input 330 (i.e., multiplyingby +1). When 286 is equal to 288, the current is steered identically tothe output nodes 340 and 342 so that the output is independent of theinput 330 and 332 (i.e., multiplying by zero). Accordingly, by mixingthe early/late pulses shown in FIG. 7B with a high input to A 330, theoutput waveform will be of the form shown in FIG. 7C. On the other hand,by mixing the early/late pulses shown in FIG. 7B with a low input to A330, the output waveform will be of the form shown in FIG. 7D.

In other embodiments, the wavelet generating function of thedifferential mixer 701 is accomplished using, for example, bridgecircuits using switches. The can be electronically controlled switchessuch as an FET-bridge mixer 702 of FIG. 7E or a diode-bridge mixer 703of FIG. 7F. In other embodiments, the switches are mechanical, using,for example, MEM (micro electromechanical machine) technology, oroptically driven switches such as a bulk semiconductor material. Invarious embodiments of the present invention, all of the ports of themixer are differential or all of the ports of the mixer accept digitalinputs, or both.

Using a differential mixer to generate the UWB wavelets according to thepresent invention provides advantages over conventional methods. Forexample, using a conventional method of passing a pulse through one ormore transmission line stubs to create a waveform includes usingcomponents (i.e., the stubs) that are not integratable. Accordingly, theconventional approach uses up more space, which is of a premium whendesigning UWB wireless devices. Accordingly, by using highlyintegratable components, such as transistor-based differentialcomponents in combination with the pulse generator 200 described above,the present invention provides a highly integratable solution forcreating UWB wavelets, even into the microwave regime.

FIGS. 8A and 8B illustrate an exemplary circuit for using a mixer 401 togenerate UWB wavelets encoded with data according to another embodimentof the present invention. As shown in FIGS. 8A and 8B, a binary NRZ datasource is connected to an input of a differential mixer 400. Connectedto the two differential inputs of the LO port 407, 408 of thedifferential mixer 401 are two outputs of a pulse generator 200providing a pair of pulse streams configured to apply an early pulse anda late pulse 410 at the second differential input 408 and a mid-pulse409, occurring between the early pulse and late pulse, at the firstdifferential input 407 of the LO port. The wavelet generator isconfigured such that the NRZ data source is at a rate such that each bitof the data will be as long or longer than the combined duration of anearly pulse, a mid-pulse, and late pulse generated by the pulsegenerator. Accordingly, each bit of NRZ data will be mixed with an earlypulse, a mid-pule, and a late pulse.

FIG. 8A illustrates the example where the incoming bit from the NRZ datasource is a ‘one,’ whereas FIG. 8B illustrates the example where theincoming data bit is a ‘zero.’ The output of the differential mixer 402for both examples is a UWB wavelet that occupies the same time frame andhas the data encoded in the shape of the wavelet, not in the timeposition of the wavelet.

FIGS. 9A and 9B illustrate the shapes of the UWB wavelets produced bythe two examples described in FIGS. 8A and 8B respectively. As shown inFIG. 9A, a UWB wavelet 900 is produced by mixing a NRZ data ‘1’ (i.e., apositive voltage) with the early pulse and late pulse 410 input to thesecond differential input of the mixer 408, and the mid pulse input tothe first differential input of the mixer 407 as illustrated by FIG. 8A.In this embodiment, the early and late pulses generated by the pulsegenerator are at one-half the amplitude of the mid-pulse generated bythe pulse generator. Accordingly, the areas of the two negative portionsof the waveform 902, 903, as shown in FIG. 9A, are each one-half thearea of the positive portion of the waveform 904. Again, as with thepositive-negative UWB wavelet described in FIGS. 5A and 5B, the shape ofthe UWB wavelet is such that the integral of the wavelet is 0.

FIG. 9B illustrates the UWB wavelet 901 produced by mixing a NRZ data‘0’ (i.e., a negative voltage) with the early pulse and late pulse inputto the second differential input of the mixer 408, and the mid pulseinput to the first differential input of the mixer 407 as illustrated byFIG. 8B. As shown in FIGS. 9A and 9B, the two different UWB wavelets areinverted representations of one another. As discussed above, by encodingthe data onto the shape of the UWB wavelet, a single bit of informationmay be encoded as one of the two shapes corresponding to a ‘0’ or a ‘1’accordingly.

FIG. 10 illustrates an exemplary UWB wavelet generator for generatingUWB wavelets that encode more than one bit of data. As shown in FIG. 10,the UWB wavelet generator uses two mixers 1003, 1004, and a summer 1005to encode two bits of NRZ data. In this embodiment, the odd bits 1001 ofthe NRZ data stream are input to a first differential mixer 1003, andthe even bits 1002 of the NRZ data stream are input to a seconddifferential mixer 1004. The first differential mixer 1003 has an earlypulse and a late pulse input to the first and second differential inputsof the LO port, respectively, as described above in FIGS. 4A and 4B. Thesecond differential mixer 1004, on the other hand, has an early pulse, amid pulse, and a late pulse 1007 input to the two differential inputs ofthe LO port, as described above in FIGS. 8A and 8B. The output of thefirst differential mixer 1003 and the output of the second differentialmixer 1004 are input to the summer 1005. Accordingly, since each of thetwo inputs to the summer 1005 can be one of two different shapes, asdiscussed above in FIGS. 5A, 5B, 9A, and 9B, the output of the summer1005 can take on one of four distinct shapes. The four distinct shapesoutput by the summer 1005 correspond to the four unique values that canbe encoded in the two bits of NRZ data (i.e., ‘00,’ ‘01,’ ‘10,’ and‘11’).

FIG. 10A illustrates an exemplary UWB wavelet generator for generatingUWB wavelets in another embodiment of the present invention. As shown inFIG. 10A, the input data stream is input to a look-up table (LUT) 1014,where the shape of the UWB wavelets is determined. Based on the value inthe look-up table 1014 corresponding to the input data stream, the twodigital to analog converters (D/A) 1010, 1012 apply amplitudeinformation onto the incoming data. The varying amplitude signals arethen mixed with the outputs of the pulse generator at the two mixers1003, 1004, as discussed in FIG. 10. Using this circuit, the incomingdata stream may be encoded into UWB wavelets having a constellation ofshapes and magnitudes which correspond to various data values accordingto the encoding scheme provided by the look-up table 1014 values.

FIG. 11 shows the two exemplary intermediate UWB wavelets generated bythe circuit of FIG. 10. As shown in FIG. 11, a first wavelet 1102results from mixing an early pulse and a late pulse 1006 with a NRZ databit of ‘1’ at mixer 1003. A second UWB wavelet 1101 results from mixingan early pulse, a mid pulse, and a late pulse 1007 with a NRZ data bitof ‘1’ at mixer 1004. Accordingly, the output of the summer 1005 will bethe addition of these two UWB wavelets which will create a UWB waveletthat corresponds to a two-bit value of ‘11.’

FIG. 12 shows four uniquely-shaped waveforms, all occurring within thesame time frame, that correspond, for example, to the four possiblevalues of the two bits encoded in the circuit of FIG. 10. As shown inFIG. 12, a data value of ‘11’ may be represented by the UWB wavelet 1201resulting from the addition of the two waveforms shown in FIG. 11. Thefour uniquely-shaped UWB wavelets 1201, 1202, 1203, and 1204 shown inFIG. 12, therefore, correspond to the four potential values of two bitsof data (i.e., ‘00, ’ ‘01,’ ‘10,’ and ‘11’).

FIGS. 13A-13D and 14A-14D further illustrate how UWB wavelets may beshaped so as to allow the encoding of further information thereon. Byadding amplitude information to the wavelet shapes already discussed,additional information may be encoded on the wavelets while stillrequiring only a single time frame to transmit the information. As shownin FIGS. 13A-13D, the wavelets produced by the circuit described inFIGS. 4A and 4B can be used to convey two bits of information if thewavelets are transmitted with one of two different amplitudes. Forexample, the wavelet illustrated in FIG. 13A may correspond to anencoded data value of ‘11,’ whereas the wavelet illustrated in FIG. 13B,having a smaller amplitude than that wavelet shown in FIG. 13A, maycorrespond to an encoded data value of ‘10.’ Accordingly, the waveletsshown in FIGS. 13C and 13D may correspond to encoded data values of‘00,’ and ‘01,’ respectively.

FIGS. 14A-14D similarly show how UWB wavelets having other shapes mayalso be further encoded with amplitude data. As would be well understoodby one of ordinary skill in the art, multiple amplitude values could beused to further encode additional bits of information, and if used in acircuit such as that described in FIG. 10, for example, an entireconstellation of values could be represented by the various shapes ofUWB wavelets generated.

FIG. 15 is a schematic of a simple, yet very fast, digital to analogdevice 1601 that can be used to apply amplitude data to either a NRZdata source or pulse streams generated by a pulse generator. As shown inFIG. 15, the simple digital to analog device 1601 uses a current mirrorcircuit 1501 to generate two current sinks, 1505 and 1507, and it usestwo differential pairs, 1520 and 1522 to steer the two currents todifferential output nodes V_(out1) 1524 and V_(out2) 1526. As a result,the circuit generates an output voltage according to table 1503. Aswould be understood by one of ordinary skill in the art, the simpledigital to analog device 1601 shown in FIG. 15 is a simple and fastdevice for generating various output voltage levels that could be usedto further encode either the NRZ data stream, or the pulse streamsgenerated by the pulse generator.

FIG. 16 is a schematic showing an exemplary circuit for using a digitalto analog converter (D/A) 1601 and a differential mixer 1602 to generateUWB wavelets having encoded thereon two bits of data. As shown in FIG.16, multiple bits (e.g., odd and even, or some other interleaved orencoding method output by an encoder 1603) are connected to the D/A1601, for example, in accordance with table 1503 in FIG. 16.Accordingly, multiple bits are encoded onto individual wavelets asamplitude and phase (0° or 180°) information.

The number of distinct amplitude values is determined by the number ofbits in the D/A and is not limited to two bits as shown in the exemplarycircuit in FIG. 16.

FIG. 17 is a schematic illustrating a circuit through which aconstellation of shapes of UWB wavelets may be generated to encode threebits of data. As shown in FIG. 17, a lookup table 1712 receives the NRZdata stream and encodes a group of data bits to drive the D/A 1601 andswitch 1705 combination. The switch 1705 is configured to select one oftwo orthogonal drive waveforms 1708, 1710 to couple to one input port ofthe mixer 1706. D/A 1601 is configured to drive various amplitudes intoanother input port of the mixer 1706. The output of the mixer 1706 is aconstellation of multi-amplitude, quadrature-phase, zero mean, UWBwavelets that are generated at extremely high rates. As would beunderstood by one of ordinary skill in the art, many variations of thecircuit shown in FIG. 17 are possible. For example, by applying a D/A toboth NRZ inputs shown in FIG. 10, more than the four phases describedcould be added to the multi-amplitude modulation to encode more bits ofinformation. Furthermore, other variations could be made to the shapesand amplitudes of the data being encoded.

FIG. 18 illustrates an approach whereby a single bit of information isencoded as a group of several wavelets (or chips), where the groupcorresponds to a unique user code 1901 (e.g., ‘0100 1010’). As shown inFIG. 18, the encoder 1900 multiplies the unique user code 1901 with eachbit of data 1902 to be transmitted. A data value of ‘0’ will be encodedas an inverted representation of the user code 1901 (e.g., ‘1011 0101’),whereas a data value of ‘1’ will be encoded as the sequence of chipsthat make up the user code 1901 (e.g., ‘0100 1010’).

FIG. 19 is a schematic of a circuit implementing the encoding schemediscussed in FIG. 18. As shown in FIG. 19, each bit of data 2001 will beinput to an exclusive OR (XOR) gate 2002 along with each bit of theN-bit user code. The output of the XOR 2002 will be the exclusive OR ofthe data (i.e., ‘0,’ or ‘1’) and the N-bit user code. Accordingly, asdescribed in FIG. 18, a data bit of ‘0’ will cause the output of the XORgate 2002 to be an inverted representation of the N-bit user code,whereas a data bit of ‘1’ will cause the output of the XOR gate 2002 tobe the same bit sequence as the N-bit user code. As would be wellunderstood by one of ordinary skill in the art, many variations of thisencoding scheme may be employed. For example, in another embodiment ofthe present invention, the N-bit user code is encoded M times for eachbit of data to be transmitted.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1-30. (canceled)
 31. A circuit for generating shaped ultrawide bandwidthwavelets, comprising: a data encoder for receiving an input data streamand encoding the input data stream into N parallel bit streams; and anencoded wavelet generator for generating an encoded M-ary waveletencoded with N bit values received from the N parallel bit streams,respectively, wherein N is an integer greater than
 1. 32. A circuit forgenerating shaped ultrawide bandwidth wavelets, as recited in claim 31,wherein the encoded wavelet generator further comprises adigital-to-analog converter for receiving one or more of the N parallelbit streams and generating an M-ary wavelet generation signal.
 33. Acircuit for generating shaped ultrawide bandwidth wavelets, as recitedin claim 32, wherein the encoded wavelet generator further comprises amodulator for modulating the M-ary wavelet generation signal with a basewavelet shape to generate the encoded M-ary wavelet.
 34. A circuit forgenerating shaped ultrawide bandwidth wavelets, as recited in claim 33,wherein the encoded wavelet generator further comprises a switchingcircuit for selecting the base wavelet shape from one or more possiblewavelet shapes based on one or more of the N parallel bit streams.
 35. Acircuit for generating shaped ultrawide bandwidth wavelets, as recitedin claim 31, wherein the encoded wavelet generator further comprises: Nmodulators for modulating the N parallel bit streams with N possiblewavelet shapes, respectively, to generate N intermediate encodedwavelets; and a summer for adding together the N intermediate encodedwavelets to generate the encoded M-ary wavelet.
 36. A circuit forgenerating shaped ultrawide bandwidth wavelets, as recited in claim 35,wherein the encoded wavelet generator further comprises Ndigital-to-analog converter located between the N parallel bit streamsand the N modulators, respectively.
 37. A circuit for generating shapedultrawide bandwidth wavelets, as recited in claim 31, wherein one of theN parallel bit streams sets the polarity of the encoded M-ary wavelet.38. A circuit for generating shaped ultrawide bandwidth wavelets, asrecited in claim 37, wherein at least one of the N parallel bit streamscomprises non-return-to-zero data.
 39. A circuit for generating shapedultrawide bandwidth wavelets, as recited in claim 31, wherein at leastone of the N parallel bit streams sets the amplitude of the encodedM-ary wavelet.
 40. A circuit for generating shaped ultrawide bandwidthwavelets, as recited in claim 31, wherein the encoder further comprisesa look-up table.
 41. A circuit for generating shaped ultrawide bandwidthwavelets, as recited in claim 31, wherein the base wavelet shape is oneof a Gaussian shape, a derivative of a Gaussian shape, and a weightedsinusoidal shape.
 42. A circuit for generating shaped ultrawidebandwidth wavelets, as recited in claim 41, wherein the weightedsinusoidal shape is one of a Gaussian weighted sinusoidal shape and aninverse-exponentially weighted sinusoidal shape.
 43. A circuit forgenerating shaped ultrawide bandwidth wavelets, as recited in claim 31,wherein the circuit is formed on as an integrated circuit.
 44. A circuitfor generating shaped ultrawide bandwidth wavelets, as recited in claim31, further comprising a filter for filtering the encoded M-ary waveletto generate a filtered M-ary wavelet.
 45. A method for generating shapedultrawide bandwidth wavelets, comprising: receiving an input data streamincluding multiple data bits; encoding the input data stream into Nparallel bit streams; generating an encoded M-ary wavelet based on the Nparallel bit streams, wherein N is an integer greater than
 1. 46. Amethod for generating shaped ultrawide bandwidth wavelets, as recited inclaim 45, wherein the generating of an encoded M-ary wavelet furthercomprises generating an intermediate wavelet generation signal inresponse to at least one of the N parallel bit streams, and wherein theM-ary wavelet is generated based on the intermediate wavelet generationsignal.
 47. A method for generating shaped ultrawide bandwidth wavelets,as recited in claim 46, wherein the generating of an encoded M-arywavelet further comprises modulating the intermediate wavelet generationsignal with a base wavelet shape to generate the encoded M-ary wavelet.48. A method for generating shaped ultrawide bandwidth wavelets, asrecited in claim 47, further comprising selecting the base wavelet shapefrom a plurality of possible wavelet shapes based on at least one of theN parallel bit streams.
 49. A method for generating shaped ultrawidebandwidth wavelets, as recited in claim 47, wherein the base waveletshape is one of a Gaussian shape, a derivative of a Gaussian shape, anda weighted sinusoidal shape.
 50. A method for generating shapedultrawide bandwidth wavelets, as recited in claim 49, wherein theweighted sinusoidal shape is one of: a Gaussian weighted sinusoidalshape and an inverse-exponentially weighted sinusoidal shape.
 51. Amethod for generating shaped ultrawide bandwidth wavelets, as recited inclaim 45, wherein one of the N parallel bit streams sets the polarity ofthe encoded M-ary wavelet.
 52. A circuit for generating shaped ultrawidebandwidth wavelets, as recited in claim 45, wherein the one of the Nparallel bit streams comprises non-return-to-zero data.
 53. A method forgenerating shaped ultrawide bandwidth wavelets, as recited in claim 45,wherein at least one of the N parallel bit streams sets the amplitude ofthe encoded M-ary wavelet.
 54. A method for generating shaped ultrawidebandwidth wavelets, as recited in claim 45, wherein the method isimplemented in an integrated circuit.
 55. A method for generating shapedultrawide bandwidth wavelets, as recited in claim 45, further comprisingfiltering the encoded M-ary wavelet to generate a filtered M-arywavelet.
 56. A ultrawide bandwidth radio, comprising: a data encoder forreceiving an input data stream and encoding the input data stream into Nparallel bit streams; an encoded wavelet generator for generating anencoded M-ary ultrawide bandwidth wavelet encoded with N bit valuesreceived from the N parallel bit streams, respectively; and a timinggenerator for providing timing signals to the encoded wavelet generator,wherein N is an integer greater than 1.